Numerous devices exist enabling a duct to be quickly connected to an intermediate coupling device, either between said duct and another duct, or between said duct and apparatus in an installation (flow control valve, actuator, . . . ), whether added to or integrated within said apparatus.
The coupling device includes means adapted, once the end of the duct has been freely inserted into a bore designed for receiving said end, to hold the end therein in sealed manner against a force tending to pull it out. In addition to having a sealing ring, said means may have members of two main types: a washer having inside teeth that are splayed apart by bending during insertion of the tube and that tend to bite into the tube so as to oppose extraction thereof; and a claw having substantially longitudinal arms whose free ends have sharp edges directed towards the outside surface of the tube and each forming a wedge that is forced into the tube when an attempt is made to pull it out, wedging being obtained by means of a camming surface provided for that purpose in the bore.
The invention relates to quick couplings including means of the first type, i.e. a washer provided with inside teeth.
Most couplings having a toothed washer include flexible teeth attached via their roots to a rigid ring which is received in a groove in the bore. The groove is generally formed between a shoulder of the bore and an insert, thereby enabling the ring to be clamped or even deformed so that the slope of the teeth is altered if the ring does not occupy a radial plane when at rest. In other cases, the groove is formed completely in an insert which is pre-fitted with the washer. In order to ensure that the force opposing insertion of the tube is not too great, it is necessary for the teeth to have a degree of flexibility so that they splay apart easily to allow the end of the tube to pass between them. Such flexibility is obtained by cutouts and recesses in the teeth, but that is detrimental to their ability to bite into the outside surface of the tube. In addition, since the teeth are relatively flexible, it is often observed that it is possible to move the tube rearwards after it has been inserted in the coupling. This rearward movement that may take place under a small traction force causes the end of the tube to be displaced within the terminal portion of the bore in which it is accurately guided. A reduction in the guidance bearing area therefore gives rise to a reduction in the quality of tube retention in the coupling. It is then observed that the tube becomes easier to ovalize, which has the consequence of reducing the quality of sealing at the coupling, and of unbalancing the forces transmitted to the periphery of the tube by the teeth, which can be a cause of untimely disconnection.
In addition, outwards displacement of the end of the tube from its housing leaves a gap between the end shoulder of the housing in the body and the end of the tube, which gap becomes a dead volume in which harmful deposits can accumulate.